Abstract
Abstract. Formaldehyde (HCHO) has been measured from space for more than 2 decades. Owing to its short atmospheric lifetime, satellite HCHO data are used widely as a proxy of volatile organic compounds (VOCs; please refer to Appendix A for abbreviations and acronyms), providing constraints on underlying emissions and chemistry. However, satellite HCHO products from different satellite sensors using different algorithms have received little validation so far. The accuracy and consistency of HCHO retrievals remain largely unclear. Here we develop a validation platform for satellite HCHO retrievals using in situ observations from 12 aircraft campaigns with a chemical transport model (GEOS-Chem) as the intercomparison method. Application to the NASA operational OMI HCHO product indicates negative biases (−44.5 % to −21.7 %) under high-HCHO conditions, while it indicates high biases (+66.1 % to +112.1 %) under low-HCHO conditions. Under both conditions, HCHO a priori vertical profiles are likely not the main driver of the biases. By providing quick assessment of systematic biases in satellite products over large domains, the platform facilitates, in an iterative process, optimization of retrieval settings and the minimization of retrieval biases. It is also complementary to localized validation efforts based on ground observations and aircraft spirals.
Highlights
Formaldehyde (HCHO) is ubiquitous in the troposphere due to its high product yields from atmospheric oxidation of volatile organic compounds (VOCs)
HCHO observations were made along the flight tracks with multiple instruments, including (1) NCAR Difference Frequency Generation Absorption Spectrometer (DFGAS) (Weibring et al, 2006, 2007, 2010); (2) Trace Organic Gas Analyzer (TOGA) (Apel et al, 2003; 2010; 2015); (3) In Situ Airborne Formaldehyde instrument (ISAF) (Cazorla et al, 2015); (4) Compact Atmospheric Multispecies Spectrometer (CAMS) (Fried et al, 2011; Richter et al, 2015); and (5) Proton Transfer Reaction Time-of-Flight Mass Spectrometer (PTR-ToF-MS) (Müller et al, 2014)
During C6, C7, and C12, HCHO is measured by two independent instruments. b Shown as green rectangles in Fig. 1. c (1) Crawford and Pickering (2014); (2) DISCOVER-AQ Science Team (2014); (3) Emmons (2016); (4) Warneke et al (2016); (5) Pfister et al (2017); (6) Richter et al (2015); (7) UCAR/NCAR – Earth Observing Laboratory et al (2016); (8) National Oceanic and Atmospheric Administration (NOAA) (2017); (9) Pollack et al (2019); (10) Hu and Permar (2019); (11) KORUS-AQ (2016); (12) Wofsy et al (2018). d TOGA has an accuracy of 15 % or better
Summary
Formaldehyde (HCHO) is ubiquitous in the troposphere due to its high product yields from atmospheric oxidation of volatile organic compounds (VOCs). This approach increases considerably the range of data and conditions that can be used for validation and reduces random noises in satellite retrievals through averaging Using this approach, Zhu et al (2016) found current HCHO satellite products are biased by −20 % to −51 % against the SEAC4RS (Toon et al, 2016) aircraft measurements over the Southeastern United States during the summer of 2013. We follow this indirect validation approach to develop a validation platform for satellite HCHO retrievals using observations from 12 aircraft campaigns all over the world, as discussed below
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